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Hello, so far it sounds like the roofers pulled the 24 volt thermostat wires loose, or turned off the power to the unit.
We can check that first, let me know what you find... we can go from there without a time limit.
Dust is not likely to be the problem.
Check the gas shut off valve located in the gas line within a few feet of the unit,
The roofers may have turned it off.
Thanks, ***** ***** in that case.
please attach a well focused, close up photo of the wiring diagram glued inside the service panel, the picture needs to be taken from straight on, in very good light.
You can use the paper clip- icon at the right end of the tool bar at the top of this dialog box to attach it here.,Include a picture of the thermostat wire connections to the printed circuit board in the same area.
If you have an error code showing, tell me what the code read out is on the wiring diagram or a sticker next to the diagram please.
If there is no paper clip-icon, look for the '+attachfiles'link at left of your send button.
I can mark it up with trouble shooting instructions.
We can go from there.
Next locate the glow plug igniter, it connects with a molex connector, unplug it, and then restart the furnace with your volt meter probes in the female glow plug igniter socket, If you are getting voltage but the igniter does not glow then the igniter is bad,
If you are not getting voltage to the igniter there are other problems we need to trouble shoot
Many of these igniters last less than 3 or 4 years, construction dust can get on them, that can cause a border line igniter to fail.
If it has a thin black line across the face of its hot surface, its bad.